Flow instability of semicrystalline polymer melt during micro-injection molding

This work investigates the flow instability of thermoplastic polymer melt that occurs on the flow front when it enters micro-cavities. On the flow front, it was observed that small balls are formed and coalesce with each other, creating many micro-weld lines. The experimental results in this work showed occurrence of this phenomenon for polypropylene and polyamide but not for high density poly(ethylene), poly(methylmethacrylate) or acrylonitrile butadiene styrene. It was found that onset of this instability is related to the spherulite size. The effects of temperature and geometry have been scrutinized. As a conclusion, the ratio of spherulite size and channel width has been proposed as a dimensionless number related to this instability. (paper)